The art of printing images with micro-fluid technology is relatively well known. A disposable or (semi)permanent ejection head has access to a local or remote supply of fluid (e.g., ink). The fluid ejects from an ejection zone to a print media in a pattern of pixels corresponding to images being printed.
To ready the head for use, manufacturers prime the disposable cartridges at the factory before shipment. (Semi)Permanent heads, on the other hand, become primed at the time of use inside an imaging device. A vacuum draws fluid from the supply item and delivers it to individual nozzles of the head. As the operation nears completion, excess fluid spills from the nozzles. The amount of fluid wasted corresponds proportionately to the number of nozzles.
After establishing the prime, systems exist to maintain backpressure throughout the imaging device. In low cost systems, or those with low page output, backpressure is commonly controlled by inserting directly into the fluid supply a foam sponge, felt piece, expandable lung, or other similar device. In more expensive systems, and those with higher page output, backpressure is routinely kept by fixing a height of the ejection head relative to a volume of fluid in the supply. As the volume varies, the height of the supply requires adjustment upward or downward. As this is often impractical, or imprecise, the backpressure is allowed to vary over the lifetime of the supply. Variable pressure, however, can detrimentally affect imaging performance.
A page wide imaging device only exacerbates the foregoing problems. As a page wide device has nozzles spanning an entire width of a print media, the amount of fluid wasted during priming operations is significantly greater than scanning style heads having shorter lengths spanning only about an inch in length, or less. The volume requirements in supply items for page wide devices are also usually greater than those for a scanning head. As taller supply tanks are the norm, the backpressure in page wide devices varies more greatly which leads to performance challenges.
Fluid flow from supply items to ejection heads can occur either with gravity feeding or pumping systems. Each has its own unique set of problems. Gravity feeding necessitates elevated positioning of supply items in an imaging device thereby increasing the size of the devices and limiting positions of supply item placement. Air locks in fluid tubing and elsewhere are also prevalent which causes imaging failure for want of sufficient amounts of fluid. Pumping systems, on the other hand, increase design complexity as dedicated pumps are required one each per the many colors of fluids channeled throughout an imaging device. Alternatively, complex clutching is necessary if but a single pump is used per the many color channels. Both gravity feed and pumping systems require significant sensors and controls to uniquely monitor and regulate their style of fluid flow. Gravity systems need floats and valves, or the like. Pumping systems need pressure monitoring and feedback devices, to name a few.
The supply item typically contains dye or pigment based ink. Dye ink is typically cheap and has broad color coverage. Pigmented ink is generally more expensive, but has a longer archival print life and higher color stability. Pigmented ink, unfortunately, is also known to settle downward over time leaving rich concentrations near a bottom of a container and leaner concentrations near a top. When printing, ink drawn from the bottom leads first to excessively densely printed colors and later to excessively lightly printed colors. The variations often result in unacceptable visible defects. The former also has the potential to clog ejection head nozzles as large particles accumulate together in micron-sized channels having fastidious fluid flow standards.
To overcome settling problems, the prior art has introduced mechanical stir bars and other agitating members that roil ink and mix sediments before and during use. While nominally effective, the approach causes expensive/complex manufacturing and necessitates motive force during use to set agitating bodies into motion. The art also has fluid exit ports raised to heights measurably higher than the floor of the container. While this avoids supplying ink to an imaging device having too dense a concentration, it prevents full use of a container's contents as appreciable amounts of ink rest below the exit port on the lowermost surfaces of the container. Still other designs contemplate both agitating members and raised exit ports. This only compounds the noted problems.
Accordingly, a need exists in the art to improve fluid control in imaging devices, especially lengthy devices spanning page widths or larger. The need extends not only to better controlling backpressure, but to eliminating wasteful practices. Avoiding artificial constraints in size, spacing and positioning of fluid structures are still further recognized needs as is eliminating complexity of design. Supplying to an imaging device an entirety of ink in a container is a concomitant need as is delivering ink with uniform concentration over a lifetime of the container. Additional benefits and alternatives are also sought when devising solutions.